Systemic Thyroid Hormone Status in Treated Graves' Disease.

Objectives: We aimed to compare the markers of thyroid hormone status in treated euthyroid Graves' patients and levothyroxine (LT4)-treated hypothyroid Graves' patients.

Methods: We collected the data of 277 patients, including 140 radioiodine-treated hypothyroid Graves' patients on LT4 treatment (group 1), 83 euthyroid Graves' patients on methimazole (MMI) therapy (group 2), and 54 euthyroid Graves' patients off MMI or radioiodine therapy for > 2 years (group 3). After the exclusion of diabetic patients, 130, 73, and 52 patients remained for analysis in groups 1, 2, and 3, respectively. Pearson and Spearman correlation coefficients were employed to assess the relationships between T3:T4 ratio and variables in each group along with univariate and multivariate linear regression models.

Results: The mean age and female/male ratio were similar in the three groups. Serum fT4 was significantly higher and T3, TSH, TPOAb, and TRAb were significantly lower in group 1 than in group 2 and combined groups 2 and 3, which translated to 27% lower serum T3:T4 ratio in group 1. Higher BMI, serum cholesterol, and LDL cholesterol and lower HDL cholesterol were observed in group 1 than in combined groups 2 and 3. In multivariate regression analysis, the T3:T4 ratio was significantly higher in combined groups 2 and 3 than in group 1 in the presence of BMI and serum fasting blood glucose, triglycerides, and TSH.

Conclusions: Hypothyroid Graves' patients using LT4 exhibited lower T3:T4 ratio despite lower TSH levels and their BMI and lipid parameters differed from those of euthyroid Graves' patients.